Self-locking telescoping device

ABSTRACT

A self-locking telescoping device including an outer tube, an inner tube telescoped into the outer tube having a cone-shaped ramp at an inboard end, and a plurality of metal spheres between the ramp and the outer tube. The metal spheres wedge between the ramp and the outer tube when the inner tube is thrust into the outer tube in a collapse direction thereby locking the tubes together. When the thrust is attributable to a severe impact, the spheres plastically deform the outer tube by plowing tracks therein thereby to absorb energy. The self-locking telescoping device further includes an actuator rod, a driver which translates the actuator in the collapse direction and in an expansion direction, a first clutch which translates the inner tube with the actuator rod in the expansion direction, a second clutch which translates the inner tube with the actuator rod in the collapse direction, and a tubular retainer on the actuator rod having a plurality of closed-ended slots around the metal spheres. The closed ends of the slots prevent the spheres from becoming wedged between the ramp and the outer tube when the second clutch translates the inner tube with the actuator rod in the collapse direction.

This is a Division of application Ser. No. 09/702,138 filed Oct. 31,2000, now U.S. Pat. No. 6,302,458 B1 issued on Oct. 16, 2001.

TECHNICAL FIELD

This invention relates to a self-locking telescoping device capable offunctioning under impact as an energy absorber.

BACKGROUND OF THE INVENTION

A motor vehicle typically includes a bumper bar and an energy absorberwhich supports the bumper bar on a body of the motor vehicle fortranslation though a relatively short energy-absorbing stroke inresponse to a low speed impact on the bumper bar. During theenergy-absorbing stroke, a fraction of the kinetic energy of the impactis converted by the energy absorber into work. In a high speed impact onthe bumper bar, however, its short energy-absorbing stroke is quicklytraversed and most of the kinetic energy of the impact is converted intowork by plastic deformation of body structure of the motor vehiclebehind the bumper bar. As motor vehicles have become more compact, theenergy-absorbing capability of their body structures has decreased dueto the smaller span between the vehicle's passenger compartment andbumper bar. A telescoping device described in U.S. Pat. No. 5,370,429supports a bumper bar close to a body of a motor vehicle except whensensors on the vehicle detect an impending impact. Then, the telescopingdevice extends the bumper bar out from the body to maximize theenergy-absorbing stroke of the bumper bar. During the energy-absorbingstroke, hydraulic fluid is throttled through an orifice of thetelescoping device to absorb a fraction of the kinetic energy of theimpact. The telescoping device described in the aforesaid U.S. Pat. No.5,370,429 is not “self-locking”, i.e., does not become structurallyrigid in compression under any circumstances, and requires a fluidreservoir and fluid seals which may leak during the service life of thedevice. Accordingly, manufacturers continue to seek improved telescopingdevices which are self-locking and which are also suitable for use asbumper energy absorbers.

SUMMARY OF THE INVENTION

This invention is a new and improved self-locking telescoping deviceincluding a stationary outer tube, an inner tube telescoped into theouter tube having a cone-shaped ramp at an inboard end thereof, and aplurality of metal spheres between the cone-shaped ramp and the outertube. The metal spheres become wedged between the cone-shaped ramp andthe outer tube when the inner tube is thrust into the outer tube in acollapse direction corresponding to a decrease in the length of thetelescoping device thereby locking the inner and outer tubes togetherand rendering the telescoping device structurally rigid in the collapsedirection. When the thrust is attributable to a severe impact on theinner tube, the spheres plastically deform the outer tube by plowingtracks therein thereby to convert into work a fraction of the kineticenergy of the impact. The self-locking telescoping device furtherincludes an actuator rod, a driver which translates the actuator in thecollapse direction and in an opposite expansion direction correspondingto an increase in the length of the telescoping device, a first clutchwhich translates the inner tube as a unit with the actuator rod in theexpansion direction, a second clutch which translates the inner tube asa unit with the actuator rod in the collapse direction, and a tubularretainer on the actuator rod having a plurality of closed-ended slotsaround respective ones of the metal spheres. The ends of the slotsprevent the spheres from becoming wedged between the cone-shaped rampand the outer tube when the second clutch translates the inner tube as aunit with the actuator rod in the collapse direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially broken-away perspective view of a self-lockingtelescoping device according to this invention;

FIG. 2 is a longitudinal sectional view of the self-locking telescopingdevice according to this invention;

FIG. 3 is similar to FIG. 2 showing structural elements of theself-locking telescoping device according to this invention in differentrelative positions;

FIG. 4 is a perspective view of the self-locking telescoping deviceaccording to this invention in a motor vehicle bumper energy absorberapplication;

FIG. 5 is a graphic representation of an algorithm controlling theself-locking telescoping device according to this invention in the motorvehicle bumper energy absorber application;

FIG. 6 is a longitudinal sectional view of a modified embodiment of theself-locking telescoping device according to this invention;

FIG. 7 is similar to FIG. 6 showing structural elements of the modifiedself-locking telescoping device according to this invention in differentrelative positions;

FIG. 8 is an enlarged view of the portion of FIG. 6 identified by thereference circle 8 in FIG. 6; and

FIG. 9 is a fragmentary perspective view of another modified embodimentof the self-locking telescoping device according to this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1-3, a self-locking telescoping device 10 accordingto this invention includes a stationary outer tube 12 having an insidecylindrical wall 14 and an inner tube 16 telescoped into the outer tubethrough an end 18 of the latter. An end fitting 20 rigidly attached tothe inner tube constitutes an inboard end thereof in the outer tube andincludes an outside cylindrical wall 22 bearing against and cooperatingwith the inside cylindrical wall 14 of the outer tube in supporting theinner tube on the outer tube for translation in an expansion direction“E” corresponding to an increase in the length of the device 10 and in aopposite collapse direction “C” corresponding to a decrease in thelength of the device each parallel to a longitudinal centerline 24 ofthe outer tube.

An annular groove 26 in the outside cylindrical wall 22 of the endfitting 20 includes a bottom 28, a small diameter end 30, and a bigdiameter end 32. The bottom 28 of the groove annular flares outward,i.e., toward the inside cylindrical wall 14, from the small diameter end30 to the big diameter end 32 and constitutes a cone-shaped ramp 34 onthe inner tube at the inboard end thereof. A plurality of hard steelspheres 36 are disposed in the annular groove 26.

During translation of the inner tube 16 in the expansion direction “E”,the spheres 36 are cupped in the annular groove 26 against the smalldiameter end 30 thereof, FIG. 2, where they slide along the insidecylindrical wall 14 of the outer tube without obstructing translation ofthe inner tube. Conversely, at the onset of translation of the innertube in the collapse direction “C”, the spheres roll up the cone-shapedramp 34 and quickly become wedged between the cone-shaped ramp and theinside cylindrical wall 14 of the outer tube thereby effectively lockingthe inner and the outer tubes together and rendering the self-lockingtelescoping device structurally rigid in the collapse direction “C”.

When the thrust on the inner tube in the collapse direction “C” isattributable to an extreme impact on the inner tube, the telescopingdevice 10 functions as an energy absorber. That is, with the steelspheres 36 wedged between the cone-shaped ramp and the insidecylindrical wall of the outer tube, and the self-locking telescopingdevice therefore structurally rigid in the collapse direction “C”, thesteel spheres plastically deform the outer tube 12 by rolling trackstherein when the thrust attributable to the extreme impact exceeds theyield strength of the material from which the outer tube 12 isconstructed. Such plastic deformation absorbs energy by converting intowork a fraction of the kinetic energy of the impact.

In a modified self-locking telescoping device 37 according to thisinvention, FIG. 9, the inner and outer tubes 16,12 are interrupted by aplurality of perforations 39. The interstices between the perforations39 constitute crush initiators. With the steel spheres 36 wedged betweenthe cone-shaped ramp and the inside cylindrical wall of the outer tube,and the self-locking telescoping device therefore structurally rigid inthe collapse direction “C”, the outer tube plastically deforms at thecrush initiators when the thrust attributable to the extreme impactexceeds the yield strength of the material from which the outer tube 12is constructed. Such plastic deformation absorbs energy by convertinginto work a fraction of the kinetic energy of the impact.

The self-locking telescoping device 10 further includes an actuator rod38 telescoped into a second end 40 of the outer tube 12 and into a bore42 in the end fitting 20 on the inner tube. The actuator rod has a rackgear 44 thereon which meshes with a pinion gear 46. The pinion gear 46is connected by a pinion shaft 48 to a prime mover in the form of anelectric motor 50 so that the motor, the pinion gear, and the rack gearconstitute a drive means operable to translate the actuator rod back andforth in the expansion and collapse directions “E”, “C” of the innertube.

A tubular hub 52 is rigidly attached to the actuator rod 38 and supportsthe actuator rod in the bore 42 in the end fitting 20 for translationrelative to the inner tube in the direction of the longitudinalcenterline 24 of the outer tube. A ring 54 is rigidly attached to thehub 52 at the end thereof facing the rack gear 44 on the actuator rodand cooperates with the inside cylindrical wall 14 of the outer tube insupporting the actuator rod on the outer tube for back and forthtranslation in the expansion and collapse directions “E”, “C” of theinner tube. An annular flange 56 on the end of the hub 52 opposite thering 54 faces an annular shoulder 58, FIG. 3, on the end fitting 20around the bore 42. A compression spring 60 seats against the ring 54and against the end fitting 20 and biases the end fitting and theactuator rod in opposite directions until the annular flange 56 seatsagainst the annular shoulder 58.

A tubular retainer 62 of the telescoping device 10 surrounds thecompression spring 60 and overlaps the gap between the end fitting 20and the ring 54. The retainer includes a hooked end 64, FIG. 2, seatedin a corresponding annular groove in the ring 54 whereby the retainer isrigidly attached to the ring and, therefore, to the actuator rod 38. Thetubular retainer has a plurality of slots 66, FIG. 1, parallel to thelongitudinal centerline 24 of the outer tube each of which terminates ata closed end 68. Each slot receives a corresponding one of the spheres36 and has a length calculated to locate its closed end 68 close to thecorresponding sphere when the spring 60 thrusts the annular flange 56 onthe hub 52 against the annular shoulder 58 on the end fitting 20, FIG.2.

The ring 54 and the spring 60 constitute a first clutch which effectsunitary translation of the actuator rod and the inner tube in theexpansion direction “E” in response to corresponding rotation of thepinion gear 46. That is, when the pinion gear rotates clockwise, FIGS.2-3, the thrust applied to the actuator rod is transferred to the endfitting 20 through the ring 54 and the spring 60 and urges the innertube in the expansion direction “E”. At the same time, the spheres 36remain cupped against the small diameter end 30 of the annular groove 26where they slide along the inside cylindrical wall 14 of the outer tubewithout interfering with translation of the outer tube. If the actuatorrod translates in the expansion direction “E” relative to the inner tubebecause of friction between the inner and outer tubes, the closed ends68 of the slots 66 in the retainer 62 separate harmlessly from thespheres 36 until the thrust on the inner tube exceeds the friction.

Conversely, the annular flange 56 on the hub and the annular shoulder 58on the end fitting 20 constitute a second clutch which effects unitarytranslation of the actuator rod and the inner tube 16 in the collapsedirection “C” in response to corresponding rotation of the pinion gear46. That is, when the pinion gear rotates counterclockwise, FIGS. 2-3,the thrust applied to the actuator rod 38 is transferred directly to theend fitting through the flange 56 and the annular shoulder 58 and urgesthe inner tube in the collapse direction “C”. At the same time, the ring54 translates with the actuator rod in the collapse direction “C” sothat the retainer 62 and the end fitting 20 translate as a unit in thesame direction. In that circumstance, the closed ends 68 of the slots 66prevent the spheres 36 from rolling up the cone-shaped ramp 34 and thusprevent the spheres from becoming wedged between the end fitting 20 andthe outer tube 14 and interfering with translation of the inner tube inthe collapse direction “C”.

Referring to FIGS. 4-5, a pair of the self-locking telescoping devices10 are illustrated in a bumper energy absorber application on aschematically represented motor vehicle 70 having a frame 72 and abumper bar 74. The outer tubes 12 are rigidly attached to the frame 72on opposite sides of thereof and the inner tubes 16 are rigidly attachedto the bumper bar. An electronic control module (ECM) 76 on the motorvehicle is connected to each of the electric motors 50 and to atransducer 78 which provides electronic signals to the ECM correspondingto the velocity of the motor vehicle. When the ECM 76 turns on theelectric motors to rotate the pinion gears 46 in the expansion direction“E” of the inner tubes, the bumper bar 74 is translated by the actuatorrods and the inner tubes from a retracted position to an extendedposition, illustrated respectively in solid and broken lines in FIG. 4,in which the bumper bar protrudes further in front of the frame 72. Whenthe ECM turns on the electric motors to rotate the pinion gears in thecollapse direction “C” of the inner tubes, the bumper bar is translatedby the actuator rods and the inner tubes from its extended position backto its retracted position.

With the electric motors 50 turned off and the bumper bar in itsextended position, a severe impact on the bumper bar 74 initiatestranslation of the inner tubes 16 of the devices 10 in the collapsedirection “C” relative to the outer tubes and the actuator rods. The endfittings 20 plunge toward the rings 54 against the resistance of thesprings 60 while the closed ends 68 of the slots 66 in the tubularretainers separate from the spheres 36, FIG. 3. The spheres then roll upthe cone-shaped ramps 34, become wedged against the inside cylindricalwalls 14 of the outer tubes, and commence plowing tracks in the outertubes to convert into work a fraction of the kinetic energy of theimpact on the bumper bar.

A flow chart 80, FIG. 5, depicts an algorithm according to which the ECM76 turns the electric motors 50 on and off including a start block 82initiated when the electrical system of the motor vehicle is turned onwith the bumper bar in its retracted position. From the start block 82,the algorithm monitors the velocity of the motor vehicle through anelectrical signal from the transducer 78 and asks at a decision block 84whether the velocity of the motor vehicle is in a high range, e.g.,above 15 miles per hour (MPH), in which a high speed impact is possible.If the answer is no, the ECM does not turn on the electric motors andthe bumper bar remains in its retracted position. If the answer is yes,the algorithm turns on the electric motors through the ECM to translatethe bumper bar 74 to its extended position more remote from the frame 72where it affords increased protection against a high speed impact.

With the bumper bar in its extended position, the algorithm monitors thevelocity of the motor vehicle through the electrical signal from thetransducer 78 and asks at a decision block 86 whether the velocity ofthe motor vehicle is in a low range, e.g., less than 10 MPH, in which ahigh speed impact is improbable. If the answer is no, then the algorithmrepeats the interrogation of vehicle velocity between the decisionblocks 84,86. If the answer is yes, the algorithm interrogates vehiclevelocity a second time after a delay of about three seconds and asks ata decision block 88 whether vehicle velocity is still in the low range.If the answer is no, then the algorithm repeats the interrogation ofvehicle velocity between the decision blocks 84,86. If the answer isstill yes, the algorithm turns on the electric motors 50 through the ECMto translate the bumper bar back to its retracted position.

Referring to FIGS. 6-8, another modified self-locking telescoping device90 according to this invention is identical to the self-lockingtelescoping device 10 described above except as now recited. Structuralelements common to the device 10 and the modified device 90 areidentified in FIGS. 6-8 with primed reference characters. In place ofthe compression spring 60 in device 10, the modified device 90 includesa retaining ring 92, an annular wave spring 94, and a thrust washer 96,FIG. 8, which constitute a preload means of the modified device. Theretaining ring 92 is supported on the end fitting 20′ on the inner tube16′ and constitutes the small diameter end of the annular groove in theoutside cylindrical surface 22′ of the end fitting. The thrust washer 96loosely encircles the cone-shaped ramp 34′ between the retaining ring 92and the spheres 36′. The wave spring encircles the cone-shaped rampbetween the retaining ring 92 and the thrust washer 96.

The pinion gear 46′ translates the inner tube 16′ of the modifiedself-locking telescoping device 90 in the collapse direction “C” throughthe actuator rod 38′, the annular flange 56′ on the hub 52′, and theannular shoulder 58′ on the end fitting 20′. At the same time, theclosed ends 68′, FIG. 8, of the slots 66′ in the tubular retainer 62′prevent the spheres 36′ from rolling up the cone-shaped ramp 34′ andbecoming wedged between the end fitting and the outer tube, FIG. 6,while maintaining the wave spring flexed in compression between thethrust washer and the retaining ring. When the pinion gear 46′ rotatesin the opposite direction to translate the actuator rod in the expansiondirection “E”, the inner tube 16′ and the end fitting 20′ remainstationary due to friction until the ring 54′ on the actuator rod seatsagainst the end fitting, FIG. 7. The ring and the end fitting thusconstitute the aforesaid first clutch of the modified device 90 whichtranslates the inner tube as a unit with the actuator rod in theexpansion direction “E”.

When the pinion gear 46′ is stationary, thrust on the inner tube in thecollapse direction “C” initiates translation of the end fitting in thesame direction relative to the actuator rod while the closed ends of theslots in the retainer 62′ separate from the spheres 36′. At the sametime, the annular wave spring 94 separates the retaining ring 92 and thethrust washer 96 to positively and substantially instantly thrust thespheres 36′ up the cone-shaped ramp 34′ into wedging engagement betweenthe end fitting and the inside cylindrical wall of the outer tube. Thespheres 36′ thus render the modified self-locking telescoping device 90structurally rigid in the collapse direction “C” unless the thrust isattributable to a severe impact on the inner tube. Then, the spheresplastically deform the outer tube by plowing tracks therein to convertinto work a fraction of the kinetic energy of the impact.

What is claimed is:
 1. A self-locking telescoping device comprising: astationary outer tube, an inner tube telescoped into the outer tubethrough a first end of the outer tube and supported on the outer fortranslation in an expansion direction and in a collapse direction, acone-shaped ramp on the inner tube at the inboard end thereof facing aninside cylindrical wall on the outer tube, an annular end wall on theinner tube at a small diameter end of the cone-shaped ramp, a pluralityof spheres between the cone-shaped ramp and the inside cylindrical wallon the outer tube cupped against the annular end wall during translationof the inner tube in the expansion direction without interfering withtranslation of the inner tube in the expansion direction and rolling upthe cone-shaped ramp into wedging engagement between the cone-shapedramp and the inside cylindrical wall on the outer tube at the onset oftranslation of the inner tube in the collapse direction thereby torender the self-locking telescoping device structurally rigid in thecollapse direction, an actuator rod telescoped into the outer tubethrough a second end of the outer tube and into the inner tube throughan inboard end of the inner tube, a drive means operable to selectivelytranslate the actuator rod in the expansion direction and in thecollapse direction, a first clutch means operable to translate the innertube as a unit with the actuator rod in the expansion direction, asecond clutch means operable to translate the inner tube as a unit withthe actuator rod in the collapse direction, and a tubular retainer onthe actuator rod having a plurality of slots around respective ones ofthe plurality of spheres each having a closed end adjacent to thecorresponding one of the spheres and engageable thereon when the drivemeans and the second clutch means translate the actuator rod and theinner tube in the collapse direction to prevent the corresponding spherefrom rolling up the cone-shaped ramp and becoming wedged between thecone-shaped ramp and the inside cylindrical wall on the outer tube. 2.The self-locking telescoping device recited in claim 1 wherein: each ofthe plurality of spheres has a hardness sufficient to plastically deformthe outer tube by plowing tracks therein when an impact on the innertube in the collapse direction exceeds the yield strength of thematerial from which the outer tube is constructed thereby to convertinto work a fraction of the kinetic energy of the impact.
 3. Theself-locking telescoping device recited in claim 2 wherein the firstclutch means comprises: a ring rigidly attached to the actuator rod, anda compression spring between the ring and the inboard end of the innertube.
 4. The self-locking telescoping device recited in claim 3 whereinthe second clutch means comprises: an annular shoulder on the innertube, and an annular flange on the actuator rod facing the annularshoulder and engageable thereon in response to translation of theactuator rod in the collapse direction.
 5. The self-locking telescopingdevice recited in claim 4 wherein the drive means comprises: a rack gearon the actuator rod, a pinion gear meshing with the rack gear, and aprime mover operable to rotate the pinion gear in a first directioncorresponding to translation of the actuator rod in the expansiondirection and in a second direction corresponding to translation of theactuator rod in the collapse direction.
 6. The self-locking telescopingdevice recited in claim 2 further comprising: a preload means operableto positively thrust each of the spheres up the cone-shaped ramp intowedging engagement between the cone-shaped ramp and the insidecylindrical wall on the outer tube at the onset of translation of theinner tube in the collapse direction relative to the actuator rod. 7.The self-locking telescoping device recited in claim 6 wherein thepreload means comprises: a retaining ring on the inner tube constitutingthe annular end wall on the inner tube at the small diameter end of thecone-shaped ramp, a thrust washer around the cone-shaped ramp betweenthe plurality spheres and the retaining ring, and a spring flexed incompression between the retaining ring and the thrust washer urging theplurality of spheres up the cone-shaped ramp into wedging engagementbetween the cone-shaped ramp and the inside cylindrical wall on theouter tube at the onset of translation of the inner tube in the collapsedirection relative to the actuator rod.